The present invention relates to an eyeglass lens grinding machine for grinding a lens to be fitted in an eyeglass frame.
A tapered edge commonly referred to as a "bevel" is formed on the periphery of an eyeglass lens so that the lens can be supported in a groove extending along an eyeglass frame. In general, a bevel corresponds in configuration to a lens by determining a curvature that conforms to the curved front surface of the lens to be processed or by dividing its edge thickness by a specified ratio.
Ordinarily, the methods described above are satisfactory but in special cases such as a lens having a strong positive or negative power and an EX lens, an increased portion of the lens will protrude from either the front or rear side of the rim on the frame in areas where the edge thickness is great and this detracts from the aesthetic appeal of the spectacles. As a further problem, if the eyeglass frame of interest has a strong curvature, the lenses that have been provided with a bevel curve by the above-described methods often fail to be fitted in the frame due to the excessive difference between the bevel curve and the curvature of the frame. In this case, forced bevelling is performed using a bevel curve in conformity with the curvature of the frame but then an even increased part of the lens will protrude from either the front or rear side of the rim on the frame in the areas where the edge thickness is great.